Recent advances in the field of compound semiconductors have given rise to a new generation of light-emitting diodes (LEDs) and lasers for the visible spectral range, particularly in the III-V nitrides-based blue and green wavelength regions. The main advantage of nitride semiconductors in comparison with other wide band-gap semiconductors is their low degradation in optical devices under high current density driving. In recent years, enormous efforts have been made by companies to enter into new house lighting and LCD back-lighting markets. The general idea is to replace conventional incandescent or fluorescent lamps by more reliable and compact semiconductor light sources, namely LED lamps. LED-based white appearance lighting aimed at replacing conventional incandescent or fluorescent lamps can be produced by a few methods such as using phosphors for down-conversion of blue or UV LEDs, and using a combination of different wavelength LEDs (such as red, green, and blue LEDs).
One of the key obstacles for market penetration is the lumens/$ cost of lamps based on LEDs. One of the common approaches is to drive an LED with the highest current density possible with minimum efficiency droop. Epitaxial growth of the LED structure to fine-tune multiple quantum wells and diffusion barriers can partially improve this efficiency droop, but good thermal management in the chip packaging to reduce the junction temperature is very critical to obtain nearly zero efficiency droop devices.
Various approaches of attaching high thermal conductivity materials onto LEDs have been adopted. Chemical vapour deposited diamond (CVD diamond), silicon carbide (SiC), aluminium nitride (AlN), and boron nitride (BN) are commonly used non-metal type sub-mounts to dissipate heat from LEDs. Copper (Cu), aluminium (Al), nickel (Ni), and CuW alloy are commonly used metal and metal alloy sub-mounts for LEDs. However, although such metal and metal alloys provide very good thermal management for LEDs, the thermal expansion coefficient (CTE) mismatch becomes an issue for device reliability after long thermal cycles of operation under high current density. CVD diamond provides excellent thermal management for LEDs, but with less satisfactory CTE matching with LEDs. Other non-metal materials such as AlN provide better thermal expansion coefficient matching, but less satisfactory thermal management.
Accordingly a need exists for LEDs and method of manufacturing LEDs having improved thermal properties.